In a previous Israeli patent application No. 101,570 filed Apr. 10, 1992 by the same applicants herein (corresponding to European Patent Application No. 93105995.0 and to U.S. patent application Ser. No. 08/043,254, filed Apr. 6, 1993, now U.S. Pat. No. 5,426,623, the specification of which is incorporated herein by reference), an optical reading head for reading data tracks of optical disks, an apparatus enabling locking, tracking and reading data from many data tracks of an optical disk were described. This device comprises an optical apparatus fox- fast addressing of tracks on the disk, optical apparatus for imaging the tracks on a detector matrix comprising a plurality of detectors arranged in parallel lines, the said detector matrix being coupled to a plurality of shift registers, on which processing of the image is possible.
The said device further comprises signal processing means to receive the data generated by the detector matrix, and to translate the said data into data contained in data spots located on the disk.
The invention described in IL 101,570 is further directed to a method of accessing and reading data from an optical disk, which method comprises the steps of:
1) providing means for illuminating the required part of the disk and acquiring the optical image of a plurality of tracks;
2) providing a detector matrix comprising a plurality of detectors, each of the said detectors being capable of producing an output signal which is proportional to the intensity of the light detected by it;
3) causing an optical image corresponding to an illuminated area to fall on the said detector matrix;
4) transferring the output signal of the said detector matrix to image processing means;
5) determining position coordinates of the track center for each data track, by analyzing the output signal of the said detector matrix;
6) saving in memory means expected track center data, comprising position coordinates of the track center located by the said analysis of the output signal; and
7) if an actually detected track center is shifted with respect to the said expected track center, electronically moving the track center position.
According to one embodiment of the abovementioned invention, at the beginning of the operation a so-called "locking" operation is carried out, to determine the track center, and the coordinates of the track center initially found are used as the first value for the expected track center. Additionally, in another preferred embodiment, a number of track center values consecutively determined are considered, to permit statistical evaluation of drift and other system parameters.
As is apparent to a person skilled in the art, the ability to move the boundaries of the data strips electronically, by redefining the position of said boundaries and without the need for mechanical adjustment, permits to compensate for drift in the disk movement. This compensation is critical for reading many tracks simultaneously, and the ability to compensate quickly for any such drift is an important feature, which permits to process large amounts of data at high rates.
The head of the device as described therein can only read data in parallel, but cannot write data in parallel on many data tracks of the disk. Therefore, writing must be done by a conventional writing head, which writes data serially, one track at a time. This is a considerable disadvantage which limits the usefulness of the apparatus, particularly in cases where writing must be done rapidly.
It is an object of this invention to provide means by which it is possible also to write data simultaneously on plurality of tracks.